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Biomedical subjects

J C Thomas

Publications and source records attributed to J C Thomas.

15 recordsLinked to original sources
PubMed1992

Characterization of the genes encoding phycoerythrin in the red alga Rhodella violacea: evidence for a splitting of the rpeB gene by an intron.

The phycobilisome of the eukaryotic unicellular red alga Rhodella violacea presents in some respects an organization that is intermediate between those of the homologous counterparts found in cyanobacteria (the putative chloroplast progenitor) and more advanced, pluricellular red algae. This suggests evolutionary relationships that we investigated at the genome level. The present work describes the sequences of two rhodophytan phycobilisome genes, rpeA and rpeB. These chloroplast genes encode the alpha and beta subunits of phycoerythrin, the major component of the light-harvesting antennae and one of the most abundant cellular proteins in these algae. The amino acid sequences deduced from both rpeA and rpeB present strong homologies with those previously reported for phycoerythrin subunits of cyanobacteria, rhodophyta, and cryptomonads. The main difference with the corresponding cyanobacterial genes was the unexpected occurrence of an intervening sequence that split rpeB into two exons. This intervening sequence presents characteristics of group II introns but lacks several structural domains. Transcriptional analyses showed that the two rpe genes are cotranscribed and that the major RNA species detected corresponds to a mature mRNA lacking the intron. As the phycobiliproteins form a group of closely related polypeptides in cyanobacteria and rhodophyta, the molecular events affecting the corresponding genes, such as the rpeB intron, may be a clue to elucidate some aspects of the molecular processes involved in the evolution of plastid genes.

Amino Acid Sequence↗
PubMed1992

Choosing an appropriate measure of diarrhoea occurrence: examples from a community-based study in rural Kenya.

Epidemiological studies which aim to identify protective or risk factors for diarrhoea may rely on any of several established measures of disease occurrence, including cumulative incidence, (CI), incidence density (ID), and point prevalence (P); each with its own strengths and limitations. Comparison of these measures was afforded by a community-based study in rural Kenya in which the incidence and prevalence of diarrhoea were measured simultaneously but by independent means in the same group of children. In a cohort study, CI and ID among 138 infants (aged 0-6 months) were 26.1% and 1.41 episodes per 100 infant-weeks, respectively. Among 111 toddlers (aged 18-29 months) CI and ID were 39.6% and 1.96 episodes per 100 toddler-weeks, respectively. In a cross-sectional study of these children, the Ps among infants and toddlers were 9.8 and 6.1%, respectively. Data on incident cases required more time and resources to obtain and evidenced more underreporting of diarrhoea episodes relative to the prevalence data. Other community-based studies have reported the ID of diarrhoea five times more often than any other measure, but appear to have calculated ID incorrectly. The infrequency with which CI and P are reported does not reflect their actual utility.

Child, Preschool↗
PubMed1992

Human immunodeficiency virus-1 seroprevalence among parturients in Los Angeles County public hospitals.

To estimate the prevalence of human immunodeficiency virus type 1 (HIV-1) among parturients in an area with a high cumulative incidence of AIDS, an HIV seroprevalence study was conducted in 1988 in Los Angeles County. Test results were available from 8485 (86.1%) of the 9860 women delivering at four public hospitals. The test results were linked to demographic and medical information available from routinely collected delivery records. Three specimens were HIV-positive, for a seroprevalence of 3.5 per 10,000. The seropositive women were all Latina. The prevalence of HIV among women delivering at all hospitals in Los Angeles County has been shown to be relatively low compared with that of other metropolitan areas with a high number of AIDS cases, such as New York city, but appears to be even lower among women delivering at public hospitals during this time period. This low prevalence is attributed to the predominance of Latinas, who may have lower levels of infection, among public hospital parturients. The relatively low prevalence of HIV among injection drug users in Los Angeles County may contribute to the overall lower prevalence among women in Los Angeles County compared with those in New York city. This study supplements county-specific data obtained from statewide blinded neonatal testing by providing details on HIV seroprevalence among the catchment populations of public hospitals in Los Angeles County.

Acquired Immunodeficiency Syndrome↗
PubMed1979

A questionnaire assessment of age differences in retention of recent and remote events.

Age-related differences in memory for recently and remotely dated events have been evaluated through questionnaire assessment. Results from previous studies employing the technique differ in the analysis of retrieval of recent and remote events. In attempting to reconcile extant results from the literature, the following study employed a group of healthy males ranging in age from 26 to 69. The results showed: 1. The elderly exhibited no impairment of the ability to remember recent colloquial events. 2. The elderly's surprisingly accurate recall of remote events was not a product of selective and frequent rehearsal.

Adult↗
PubMed1978

Prazosin and clonidine for moderately severe hypertension.

In a single-blind comparative study of the cases of 30 moderately hypertensive patients, clonidine hydrochloride and prazosin hydrochloride had similar effectiveness in lowering blood pressure. Neither agent had significant effects on the renin-aldosterone axis. Addition of polythiazide to prazosin and chlorthalidone to clonidine notably increased the antihypertensive effect of both drugs. Serum cholesterol levels were observed to decrease when prazosin and clonidine were given and to rise when the diuretics were added to the regimen. The patients treated with clonidine were troubled by side effects, particularly drowsiness and dry mouth. Prazosin was better tolerated, with side effects tending to diminish with time. The "first-dose" effect was seen in two patients given prazosin, but it did not limit treatment. Both diuretics induced notable hypokalemia.

Adult↗
PubMed1978

Age-related differences in serial binary classification.

In a two-choice serial task, three groups of subjects with median ages of 37, 54, and 69 years pressed one response lever when the current signal was the same as its immediate predecessor in a sequence, and the other when it was not. Four classes of events-same signal/same response, same signal/different response, different signal/same response, different signal/different response-occurred equally often. The reaction times of subjects in the oldest group exceeded those of the two younger groups by a constant amount under all conditions; there was no evidence that stimulus or response repetition interacted with age. The data from all age groups support only the hypothesis that repeating a given signal is sufficient to produce the repetition effect in a choice reaction task.

Adult↗
PubMed1978

Age and familiarity in memory scanning.

Sixty-five healthy males (31 to 75 years old) memorized lists of six letters (familiar or unfamiliar organization). Letters were then presented singly, and subjects responded yes or no according to whether a given letter was in the memorized set. Subjects of all ages took longer to respond in the case of the unfamiliar list. This was disproportionately true for the oldest subjects, consistent with the idea that the age-related differences in the unfamiliar condition could not be wholly accounted for by psychomotor factors. The distributions of response latencies in the oldest groups had greater variance and skew.

Adult↗
PubMed1978

Retrieval time from different memory stores.

Two experiments were carried out to measure age-related differences in speed of error-free recall by normal adults. The major results were that: (a) the time taken to read a word aloud (retrieval from lexical memory) does not increase appreciably until subjects reach their 60s; (b) the time taken to recall a verbal item just attended to (retrieval from primary memory) increases steadily throughout the adult years, and most markedly between the sixth and seventh decades; and, (c) the time taken to recall recent verbal information outside the span of attention (retrieval from secondary memory) also increases as a function of chronological age, at a relatively rapid rate and most markedly between the fifth and sixth decades. The effects are independent of the number of stimulus-response alternatives.

Adult↗
PubMed1977

Maximal aerobic power in women cadets at the U.S. Air Force Academy.

A sample of 17 women cadets of the U.S. Air Force Academy's Class of 1980 was assessed to determine their maximal oxygen consumption and percent body fat. The sample was selected using the ponderal index to insure a stratified sample of body types. The Short Balke protocol was used to determine Vo2 max, and the Siri and the Keys and Brozek equations were used to find percent body fat. The Katch and McArdle equation was employed to determine body density. The average Vo2 max for the women cadets was 46.1 ml/kg/min (S.D. = 4.0). Correcting for altitude, this value compares quite favorably with other reported values. The 24.8% mean body fat places these subjects well within the normal range for college age females. The female cadets of the Class of 1980 appear to be above their contemporaries in civilian life in circulo-respiratory fitness.

Adipose Tissue↗
PubMed1977

Age-related differences in naming latency.

Older people seem to have difficulty learning new materials, perhaps because it takes them longer to retrieve relevant encoding information from memory. To assess the effects of age on speed of retrieval, 60 healthy males from 25 to 74 were shown pictures of common objects they were to name aloud as quickly as possible. The older subjects took longer to name the pictured objects. This difference was minimized with practice or when the name was cued, but did not interact with word frequency. The pattern of results for healthy older subjects was not similar to that found by Wingfield for brain-damaged subjects.

Adult↗
PubMed1976

Effects of age and frequency of stimulus repetitions on two-choice reaction time.

Binary choice-reaction times for 123 males, 25-79 years of age, were obtained in a sequence of discrete trials in which the proportion of occasions that the same stimulus was presented twice in succession varied from .25, .50, and .75 or from .75, .50, and .25 over successive thirds of the sequence. Stimulus alternations were responded to more rapidly than stimulus repetitions by subjects in all age groups, especially in trial blocks with .75 alterations. The absolute differences in mean reaction time to stimulus alterations and repetitions increased with age. The results are consistent with the hypothesis that reaction times are affected both by pre-existing expectations for stimulus alternations as well as expectations for stimulus alternations or repetitions developed during the course of the experiment. Mean response latency as well as between- and within-subject variability in performance increased with age. Analyses of frequency distributions of the reaction times indicated that the psychomotor component of reaction time increases with age while the decision-making component becomes more variable.

Adult↗
PubMedDate not supplied

High-resolution particle size analysis in biotechnology process control.

Many industrially important proteins can now be expressed intracellularly as insoluble protein inclusion bodies. In production, large-scale centrifugation is commonly used to separate and recover the inclusion bodies. Recovery efficiency depends critically on the centrifuge feed rate, which must be optimized to minimize production costs. We have used a disc centrifuge photosedimentometer to make high-resolution measurements of the particle size distribution (PSD) of the supernatant during the production of porcine somatotropin (pST) inclusion bodies. These measurements readily monitor the breakthrough of inclusion bodies into the supernatant and allow the centrifugation operation to be optimized.

Biotechnology↗